Penetrating recording microelectrode arrays are a crucial component of numerous human neuroprosthetics. Obtaining selective, high fidelity, long-lasting readouts of brain activity is a critical technology across basic and applied neuroscience that impacts learning and memory studies as well as motor, pre-motor, and visual cortex neuroprostheses and brain-computer interfaces. However, implantation of cortical microelectrodes causes a reactive tissue response, which results in a degradation of the preferred functional single-unit performance over time, thus limiting the device capabilities. Insertion of neural probes or microelectrodes inevitably disrupts the blood-brain barrier (BBB) integrity and causes microhemorrhages that have been shown to trigger the inflammatory tissue response cascade. The degree of microhemorrhaging from probe insertion has been shown to be uncontrollable and difficult to reproduce across implants, mirroring the large variability in inflammatory tissue responses and chronic recording success. We hypothesize that the level of BBB damage impacts chronic neural recording quality. This proposal aims to characterize the sustained BBB breakdown and chronic recording failure in vivo caused by the insertion induced BBB disruption and BBB occlusion by quantifying structural, cellular, and molecular level tissue response to chronic implants in the brain in real time through combining multiphoton imaging technology and neural engineering technology at the University of Pittsburgh. A dynamic understanding of the interfaces is necessary for elucidating the mechanism(s) behind neural recording failure. This work has the potential to output basic and clinical science level knowledge relevant to neural engineering, ischemia, stroke, intracortical hemorrhage, aneurysm, traumatic brain injury, and closed-loop neurostimulation.